functional-tester/rpcpb: simplify "return err"
functional-tester/rpcpb: simplify "return err"

Signed-off-by: Gyuho Lee <3454051ee3341eb69bdf6fca40899cdad4d86496@gmail.com>

dannysauer/etcd,etcd-io/etcd,mqliang/etcd,joshix/etcd,bdarnell/etcd,mkumatag/etcd,vimalk78/etcd,rnaveiras/etcd,bdarnell/etcd,xiang90/etcd,sinsharat/etcd,mqliang/etcd,mkumatag/etcd,gyuho/etcd,xiang90/etcd,glevand/coreos--etcd,sebrandon1/etcd,mkumatag/etcd,rnaveiras/etcd,gyuho/etcd,ajityagaty/etcd,mqliang/etcd,etcd-io/etcd,fanminshi/etcd,li-ang/etcd,cockroachdb/etcd,glevand/coreos--etcd,etcd-io/etcd,rnaveiras/etcd,sebrandon1/etcd,cockroachdb/etcd,coreos/etcd,coreos/etcd,ajityagaty/etcd,ajityagaty/etcd,lorneli/etcd,lorneli/etcd,li-ang/etcd,dannysauer/etcd,fanminshi/etcd,joshix/etcd,vimalk78/etcd,sinsharat/etcd